1. Field of the Invention
The present invention relates to a light source connected to an endoscope, for providing light to the endoscope.
2. Description of Related Art Statement
There are several types of endoscopes such as medical endoscopes, used for observing viscera in a body cavity or industrial endoscopes for observing the inside of boilers, turbines, engines, or chemical plants. In order to perform examination or observation by means of the above endoscopes, additional peripheral devices such as a controller, light source, and monitor are required.
In a conventional device for providing light to an endoscope, a lamp acting as a light source, such as a xenon lamp, is supported with a heat sink and electric power is supplied to the lamp via the heat sink.
When a lamp of such an apparatus is replaced, operation of lamp replacement must be performed after a lamp-exchanging door is opened and the lamp is removed from the apparatus together with a heat sink. Such operation is dangerous because there is some possibility for an operator to get an electric shock. In order to avoid this, an interlock switch is usually provided so that the electric power supply may be cut off when the lamp-exchanging door is opened. Another interlock switch is also provided so as to discharge the charges stored in a capacitor connected to the amp in parallel.
FIG. 1 is a schematic diagram showing a configuration of a lamp drive circuit in a conventional light source device.
The lamp drive circuit of this light source device has a switching regulator 4 acting as a power supply circuit for a lamp, which is connected to an AC power line 1 via a fuse 2 and first interlock switch 3. This interlock switch 3 acts in conjunction with a lamp-exchanging door so that whenever the lamp-exchanging door is opened the interlock switch 3 breaks the circuit so as to interrupt power supply to the switching regulator 4. The switching regulator 4 includes a transformer 5 composed of an inverter transformer, in which reinforced insulation is provided between the secondary and primary circuits to ensure safety. The secondary output of the switching regulator 4 is connected to a xenon lamp 7 via a starter 6 for generating a high voltage required for turning on the xenon lamp. Furthermore, a second interlock switch 9 and a discharging resistor 8 are provided between the switching regulator 4 and the starter 6 in such a manner that the second interlock switch 9 may connect between two terminals on the secondary side via the discharging resistor 8 so as to discharge the charges stored in a capacitor disposed in the secondary circuit.
The second interlock switch 9, as in the case of the first interlock switch 3, operates in conjunction with the amp-exchanging door so that when the lamp-exchanging door is opened the second interlock switch 9 may make the secondary circuit closed via the discharging resistor 8 so as to discharge the charges stored in the secondary circuit.
However, in the conventional light source device described above, a large size is required for the first interlock switch 3 to directly shut off the connection of the power line in the primary circuit, thus a large space is also needed for installation of the first interlock switch 3.
Moreover, in order to avoid electric shock due to the charges stored in the capacitor in the secondary circuit during a lamp replacement operation, another space is also required for the installation of the second interlock switch 9 for discharging the charges stored in the capacitor. As a result, the size of the entire device becomes excessively large.
Furthermore, reinforced insulation is required in the structure of the transformer 5 of the switching regulator 4 so that the possible failure of the interlock switches may not result in the reduction of safety. A minimum of 8 mm is needed in the creepage distance, and a minimum of 5 mm is required in the space distance so as to ensure the insulation between the primary and the secondary circuits meets safety standard requirements, which results in the large size of the transformer. Referring to FIG. 2 which shows the structure of the transformer 5, the widths of interlayer tapes 13 and spacer tapes 14 must be sufficiently large to obtain a required creepage distance between the primary windings 13 and secondary windings 12. Thus, the transformer 5 becomes large in size.
As described above, large space is required for installing the first and second interlock switches so as to ensure safety, which results in the large size of the transformer, which further results in the difficulty of reduction of the size of light source device.